The UK triathlon season closed on 20 September with IRONMAN 70.3 Weymouth. The off-season is when most people decide what they’re racing next year, and more of those people than ever are signing up for their first triathlon.
That matches what we’re seeing in Hertfordshire and North London. More of the swimmers getting in touch are new to triathlon, and a surprising number are aiming at a race abroad.
This post covers three things: what’s happening in UK triathlon, the races people are entering, and how to prepare for the part of a first triathlon that worries most people. That part is the swim.
UK triathlon is growing again, and the growth is first-timers
Going into 2026, around 120,000 people in Great Britain are actively racing triathlon. That’s still below the sport’s peak, but the direction has changed. Industry figures from the Triathlon Industry Association show registrations rising in early 2026, with new entrants younger and less experienced than the traditional field. (source)
The same shift shows up in race data:
- Under-30s: IRONMAN UK reported a 63% rise in under-30 participants in 2025. (source)
- First-timers: across Supertri’s events, which include Blenheim, 41% of 2025 entrants were racing their first triathlon — and Supertri is targeting 10,000 more first-timers in 2026. (source)
- Women: women now make up more than a third of UK race participants, and the industry is actively working to grow that. (source)
Put simply, the typical new triathlete in 2026 is a fit runner or gym-goer who can swim but has never raced in open water. That’s exactly who the swim leg catches out.
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Check coaching availability →The races people are choosing
In the UK
Blenheim Palace Triathlon (June, Oxfordshire). The UK’s largest triathlon, with around 7,000 amateurs across the weekend. The swim is in the palace’s lake, over 400m (Super Sprint) or 750m (Sprint). Its size and short swim distances make it one of the most popular first races in the country. (official site)
London T100 (July, Royal Docks). The nearest major mass-participation race to North London and Hertfordshire. It’s based at ExCeL, with the swim in Royal Victoria Dock and distances from Super Sprint up to the full T100. (official site)
IRONMAN 70.3 Swansea, Bolton and Weymouth. These are the step-up races for athletes moving to middle distance, with a 1.9km swim in a dock, lake or sea respectively. They aren’t usually first races, but they’re often the second-season goal.
Closer to home
You don’t need to travel to race your first triathlon. Hertfordshire has three good starting points:
- HSV Sprint Triathlon, Hatfield. A 400m pool swim with swimmers set off at intervals, fastest first. It’s the gentlest possible introduction, with no open water and no mass start. (details)
- Hertfordshire Triathlon, Stanborough Lakes. A lake swim, and home to the county club championships. (details)
- ATW Hertfordshire & Middlesex Triathlon. A swim in a private lake that’s normally closed to the public, with distances from Super Sprint to Standard. (details)
A sensible progression for a first season is a pool-swim triathlon first, then a lake race.
Abroad: the winter-sun races
The trend we didn’t expect is how many UK athletes are building towards a race abroad, often in the UK off-season.
Dubai T100 (November). Around 8,000 athletes raced across the 2025 weekend. The 2026 edition runs 13–15 November at Al Mamzar, with distances including Olympic and the full T100. (official site)
IRONMAN 70.3 Doha (March 2027). A new race with a warm sea swim at Old Doha Port. (details)
Mallorca, Lanzarote and Roth. These have been the long-standing British favourites for years, combining good weather, big crowds and easy flights.
The swim is where first races go wrong
Most first-time triathletes aren’t weak swimmers. They’re pool swimmers. The swim leg exposes the gap between the two, and it tends to show up in four ways.
1. The start. A pool session starts calmly from the wall. A triathlon starts with dozens or hundreds of people in the water together, arms everywhere, often in water you can’t see through. Heart rate spikes, breathing goes short, and many first-timers end up on their back or breaststroking within the first 100 metres. It isn’t a fitness problem. It’s an unrehearsed situation, and you can rehearse it.
2. Sighting. There are no lane ropes and no black line. If you can’t lift your eyes to spot a buoy without breaking your stroke, you’ll swim further than the course, sometimes much further.
3. Pacing. Adrenaline makes everyone start too fast. In a sprint triathlon, the swimmer who goes out steady and builds usually exits the water ahead of the one who sprinted the first 200m, and with more left for the bike.
4. The pool-to-open-water gap. Cold, wetsuits, chop and murky water all change your stroke. Swimmers who have only ever trained indoors often find their technique falls apart in their first open-water swim.
Racing abroad? Check whether you’ll be allowed a wetsuit
This one catches UK athletes out every year.
Most British triathletes do all their open-water training in a wetsuit. A wetsuit lifts the hips and legs, which hides a lot of technical weaknesses. Warm-water races often don’t allow them, and the temperature that decides it is lower than most people think.
Under World Triathlon rules the cut-off depends on how far you swim. For swims up to 1500m — super sprint, sprint and standard distance, which covers almost every first triathlon — wetsuits are forbidden once the water reaches 22.0°C. Only on swims of 1501m and longer does the limit rise to 24.6°C. (source) So a warm British summer lake, or any race in a hot country, can put a short-course swim over the line while an Ironman swim in the same water stays wetsuit-legal.
The Dubai T100 organisers predicted water of 26–27°C for their 2025 race, which is above both limits. (source) Always check the current athlete guide for your race, because organisers’ rules differ and some set their own thresholds.
If your race is non-wetsuit, expect three changes:
- Your legs will sit lower. Body position and kick timing, which the wetsuit was covering up, suddenly matter.
- Your pace will be slower than you’re used to. Plan your pacing on non-wetsuit swims, not wetsuit swims.
- Your pull buoy has been hiding the same problem. If most of your pool sets are with a buoy, you’ve been training the same buoyancy you won’t have on race day.
The fix is technical, not fitness. It comes down to body position, kick and rehearsing race pace without assistance, and the UK winter is the right time to do it.
A simple plan for your first triathlon swim
If your first race is next summer, here’s a sensible outline:
- Now to December: pool technique. Get your freestyle efficient enough that 750m feels controlled, not survived. Video analysis is the fastest way to find out what is actually happening in your stroke.
- January to March: build continuous swimming, practise sighting in the pool, and swim some sets with no wall push-offs.
- April to race day: open water as soon as venues open, in a wetsuit if your race allows one. Rehearse the start, sighting and your pacing.
For a winter race abroad, compress this into the 10–12 weeks before race day and put non-wetsuit work at the centre of it.
Is triathlon swim coaching right for you?
Our triathlon swim coaching is for people who are new to triathlon, not new to swimming. If you can swim continuous lengths, any stroke, we can make your first race swim calmer, straighter and faster. If you can’t yet, this isn’t the right service for you.
We coach triathletes across Hertfordshire and North London, from first Super Sprint to Ironman. Tell us your race, your distance and your date, and we’ll match you with a coach and build the swim around it.
Race details correct at the time of writing (September 2026). Always check the official event website for current dates, distances and rules.